The highly invasive prohibited weed has been illegally sold at regional markets in the past and poses a threats to rivers, dams and irrigation channels.

It is the dangerous potential of the species that has prompted authorities in both Victoria and NSW to warn people about it.

There is particular concern for the Yarrawonga and Corowa regions and especially Lake Mulwala.

The Victorian Department of Environment and Primary Industries is asking people in the Yarrawonga region to report sightings of the prohibited weed.

Biosecurity officer Kate Cunnew said water hyacinth was considered one of the world’s worst aquatic species and an infestation could double its size within two weeks, devastating natural waterways and impacting heavily on aquatic flora and fauna.

“Water hyacinth can be distinguished by its purple flower spikes in summer and thick, fleshy round leaves that sit on the water’s surface, while its long roots trail in the water below,” she said.

“The plant has been unlawfully sold at regional markets in the past and the department is concerned residents may have innocently bought some of the ‘pretty plants’ for their fish tanks, ponds or dams.

“It’s vital the public report if they have seen or purchased this plant to ensure the department can proactively protect our waterways, such as Lake Mulwala.”

It grows prolifically in the summer months, but its large, round leaves make is distinctive at any time.

The weed was discovered in Albury several years ago and has recently been found in ponds at Euroa and Seymour and a drain at Tongala.

Ms Cunnew said the weed preferred still water and could quickly take over dams or irrigation channels.

She has urged people not to attempt to rid areas of the weed and leave eradication to the department for safe and secure disposal.

In Victoria, the invasive aquatic species is a prohibited weed under the Catchment and Land Protection Act 1994 and in NSW it is declared as a class two weed under the Noxious Weeds Act 1993.

Anyone who has seen the plant growing in NSW can contact Corowa Council weed officer Pat Minogue on 0427 929 597.